We will continue our studies of sudden death occurring a long time after surgery by studies of the conduction system. We will continue our studies of unexpected sudden death in otherwise clinically healthy young people by similar conduction system studies. We will continue our studies of congenital heart block by conduction system studies and of WPW by serial section studies of both AV rims and the conduction system. We will study the conduction system and its nerve supply in atrial arrhythmias. We will study the pathology of the summit of the ventricular septum in the aged and relate this to electrocardiographic and conduction system studies. We will continue to describe and study the congenitally abnormal hearts of the Chicago area. We will codify all our congenital hearts seen in the last 20 years and synthesize them into a book. We will initiate the study of the histology of the coronary arteries in congenital heart disease. We will study the relative incidence of various types of congenital heart disease in our material in the last twenty years.